Method of and apparatus for erasing

ABSTRACT

A method of removing radiation-absorptive material from a base which is relatively nonabsorptive of the radiation. A short pulse at such energy level and in the order of milliseconds or less is generated and directed against the absorptive material. Energy is absorbed by the absorptive material to affect its heating and removal from the base. The base absorbs substantially a minimal amount of radiation and thus remains substantially intact.

United States Patent to H0 A.C.

Inventor Arthur L. Schawlow 839 Esplanada Way, Stanford, Calif. 94305Appl. No. 784,977

Filed Nov. 7, 1968 Patented Jan. 5, 1971 Continuation of applicationSer. No. 471,811, July 18, 1965, now abandoned.

METHOD OF AND APPARATUS FOR ERASING 7 Claims, 2 Drawing Figs.

U.S.Cl 219/121 Int. Cl 823k 9/00 Field of Search 219/121 [56] ReferencesCited UNITED STATES PATENTS 3,305,666 2/l967 Zaromb 219/383 3,314,0734/1967 Becker 346/76 Primary Examiner-J. V. Truhe Assistant ExaminerLawrence A. Rouse Attorney-Paul B. Fike ABSTRACT: A method of removingradiation-absorptive material from a base which is relativelynonabsorptive of the radiation. A short pulse at such energy level andin the order of milliseconds or less is generated and directed againstthe absorptive material. Energy is absorbed by the absorptive materialto affect its heating and removal from the base. The base absorbssubstantially a minimal amount of radiation and thus remainssubstantially intact.

PATENTEU JAN 5 I97! ARTHUR L. SCHAWLOW BY M @ML PATENT AGENT METHOD OFAND APPARATUS FOR ERASING The present application constitutes acontinuation of applicants prior application Ser. No. 471 ,81 l filedJuly 14, I965.

The present invention relates generally to erasure techniques and moreparticularly to a method of and apparatus for erasing printed ortypewritten characters from paper or some other base. The inventiondescribed herein was made in the performance of work under a NASAcontract and is subjected to the provisions of section 305 of theNational Aeronautics and Space Act of 1958, Public Law 85-668 (72 Stat.435; 42 U.S.C. 2457).

Most individuals, and secretaries in particular, are aware of thetroublesome nature of making erasures of a typewritten letter or othercharacter from the paper. Conventionally, a rubber eraser is employed bythe secretary or other individual to remove the undesired letter with arubbing, abrasive action. Considerable time is consumed if the erasingeffort is to be effective, particularly since movement of the typewriterplaten is usually necessary and, if multiple copies are being typed,additional sheets of paper must be inserted between the copies to avoidsmudging thereof. The abrasive action leaves a residue includingparticles of the eraser, the pigment and the paper as well, and theseparticles frequently drop into the working mechanism of the typewriterto subsequently interfere with its optimal operation. Finally, uponcompletion of the erasure, an abraded section of paper which is clearlyvisible remains, thus to spoil the overall appearance of the finallytyped page,

Accordingly, it is the general object of the present invention toprovide a novel erasing method and apparatus whichfunctions in a neatand rapid fashion so as to overcome all of the mentioned difficulties.

More particularly, it is a feature of the invention to provide a methodof erasing which employs radiation as the operating mechanism. I

Yet more specifically, it is a feature of the invention to employcoherent radiation to perform the erasing function so that precisecontrol of the area to be erased can be achieved.

It is a particularly significant feature of the invention to provide anerasing method utilizing a short pulse of radiation which is highlyabsorbed by the pigment or other material to be erased so as to effectrapid localized heating and subsequent vaporization thereof.

As a correlated feature of the invention, the radiation is chosen so asto be highly reflected by the paper or other base upon which the printedpigment appears to that the entire process is substantially notdestructive of the paper.

Quite specifically, it is a feature of the invention to utilize a shortpulse of coherent radiation from a laser operating at a predeterminedpower level to carry out the erasing function.

Accordingly, a correlated feature of the invention is the provision ofan erasing apparatus which utilizes a laser conveniently mounted fordirecting its beam accurately onto the area where the erasure is tooccur.

Another feature of the invention relating to the apparatus is theprovision for adjustment of the erasing beam so that, for example,typewritten characters of various sizes (e.g. pica or clite type) can beaccurately erased.

These as well as other objects and features of the invention will becomemore apparent from a perusal of the following description of a preferredmethod for practicing the invention and an exemplary apparatus forcarrying out such method in practice.

In its most general terms, the method of the present invention involvesfirst, the generation of radiation at a desired frequency and a chosenpower level and then directing such radiation as a beam of controlledsize mite area of paper or other base material on which the character tobe erased appears. To facilitate understanding, the method and apparatuswill both be described in connection with one simple, obviousapplication, that of erasure of a single typewritten character composedof carbon pigment which has been previously ap plied to a sheet ofstandard white paper. However, it will become apparent from thefollowing detailed description that many other specific materials can beerased or-removed by substantially the same process and no limitationsare therefore to be inferred.

More particularly, the steps of the method involve preferably thegeneration of a beam of coherent radiation preferably in the lightportion of the frequency spectrum which generally includes ultraviolet,visible and infrared waves. Such a beam is readily produced by a lasersuch as is briefly described hereinafter and in more detail in US. Pat.No. 2,929,922, issued Mar. 22, 1960. The precise frequency ofoperationcan vary within limits, but should be controlled so that maximumabsorption by the pigment and minimum absorption (or maximum reflection)by or paper occurs. No particular difficulty is experienced whenconventional black colored carbon pigment characters appear on whitepaper since the black carbon approaches in character the so called blackbody" which has percent absorption in the light spectrum whereas thewhite paper is highly reflective.

Regardless of the precise frequency chosen, the beam of coherentradiation is highly directional, consisting of waves havingsubstantially planar wave fronts so as to be highly directive andtherefore easily controllable. Preferably, the beam is focused by aconvex lens or the like so as to be accurately directed onto the areaoccupied by the character to be erased. Typically, an ordinary characterproduced by a conventional typewriter occupies an area of 0.1 squarecentimeter so that a slightly convergent focusing of a typical laserbeam can readily be adapted for accurate coverage of such an area.

Although th'earea exposed to the laser beam can be controlledaccurately, an additional shielding step can be em ployed to mask offsurrounding areas and thus effectively preclude erasure of neighboringtyped characters.

When the beam is directed against the exposed area, the highly absorbentcarbon pigment is rapidly heated so as almost instantaneously tovaporize whereas the surrounding paper which is highly reflective isheated but slightly and remains substantially undamaged. In addition tothe vaporization, it is believed that some burning (oxidation) of thevaporized carbon may take place. Regardless of the precise mechanism, noresidue appears and a clean, white, undamaged section of paper remainsfor retyping of the proper character thereon.

To assure that the paper remains undamaged, it is preferred that thepulse of radiation be extremely short, in the order of milliseconds orless, and that the power level of the radiation be approximately in therange of 5 to I00 kilowatts per square centimeter. While the length ofthe pulse and the power level can of course vary depending upon theprecise characteristics of the paper or other base and the pigmentthereon, the ranges specified hereinabove have been determined asextremely satisfactory for removing black carbon pigment from ordinarywhite stationery to provide effective erasing with no accompanying paperdamage. In order to practically carry out the steps of the method asspecified hereinabove, an exemplary apparatus can take the formillustrated in the accompanying drawing wherein: a

FIG. 1 is a fragmentary perspective view of an erasing apparatus mountedon'a conventionaltypewriter, and

FIG. 2 is an enlarged fragmentary perspective view of a laser formingpart of the apparatus illustrated in FIG. I.

With initial reference to FIG. 1, the laser, indicated generally at 10,is mounted at one end of an arm 12 whose 0pposite extremity is pivotedat one side of a typewriter T for movement about a vertical axis so thatthe entire laser structure can be moved from an inoperative positionadjacent one side of the-typewriter to the illustrated central operativeposition over the keyboard whereat the laser beam is directed preciselytoward a character centered on the typewriter. Thus, when such characterhas been erased by the radiation impinging thereagainst, the typist isimmediately ready to continue by typing the correct character.

While the laser 10 itself is known and its detailed characteristics aredescribed in the aforementioned US. Pat. No. 2,929,922, the illustratedlaser, quite briefly can be described as including an outer housing 14of generally cylindrical configuration, preferably having a reflectiveinterior so that light generated by several flash lamps 16 supportedtherewithin on suitable spacers 18 is directed substantially toward theaxis of the housing whereat a negative temperature medium is supported.While various materials can be utilized, it is known that greaterintensities can be obtained with solid materials such as the ruby rod 20illustrated which is essentially a cylindrical rod of aluminum oxidecontaining 0.05 percent of chromium oxide. As described in detail in theaforementioned U.S. Pat., No. 2,929,922, the ends of the ruby rod 20 areprovided with predominantly reflective coatings 22, 24 which can be thinlayers of gold. The coating 24 on the right must be relatively thin soas to have slight transmission capabilities so that a beam generatedwithin the ruby rod 20 when the lamps are flashed emerges from the rightof the structure as a highly directive beam indicated at B whosefrequency is approximately 6,943 Angstrom units at room temperature. Thelamps 16 are energized by discharge of a suitable capacitor bank chargedto a DC voltage of approximately 900 volts from a suitable l l() volt ACsource, all of this material being preferably housed in a separate boxindicated at 26 which may be placed at any convenient location adjacentthe typewriter T and connected to the laser structure itself by suitableconnecting wires 28. A suitable pushbutton 29 on the laser is depressedto instigate operation.

The highly directive, pencillike beam B of radiation emanating from thelaser 10 is preferably directed through a convex lens 30 and theconvergent beam emanating from the lens is directed against the typedcharacter C whose erasure is desired. Preferably, after passing throughthe lens 30, the convergent beam also passes through a generallyrectangular aperture in a shield 32 located closely adjacent to thetyped character which is to be erased, the material of the shield beinghighly absorbent to the radiation so as to effectively preclude passageof any misdirected radiation against adjacent printed characters on thepaper. Both the shield and the lens are suitably mounted in a taperedextension of the main cylindrical housing 14 of the laser.

In order to accommodate different type sizes, the entire laser housingis preferably mounted slidably in a sleeve 13 carried by the arm 12 forlongitudinal or axial adjustment, a simple adjustment screw enabling thetypist to make such adjustment quickly and easily when needed.

A typical beam emanating from the described laser 10 can,

,for example, produce a pulse having a length of one-half millisecondand a total power of 2 kilowatts so that a total energy .of one joule isdirected against the area occupied by the typed character on the paper,such area as previously mentioned being approximately 0.1 squarecentimeter. Such a pulse provides effective erasure with no paper damagewhatsoever and obviously requires but very little power expenditure.

It will be apparent that the detailed structure described immediatelyhereinabove and the more detailed steps of the method need not befollowed precisely to fall within the scope of the present inventionand, accordingly. the foregoing description is to be construed as purelyexemplary and not in a limiting sense, and the actual scope of theinvention is to be indicated only by reference to the appended claims.

lclaim: I 1. The method of removing radiation-absorptive material from abase which is relatively nonabsorptive of the radiation which comprisesthe steps of:

generating a short at such energy level and pulse in the order ofmilliseconds or less of substantially coherent radiation; and

directing such radiation against the absorptive material whereby energyis absorbed therein to effect a heating and removal thereof from thebase, the base absorbing substantially a minimal amount of radiationwhereby it remains substantially intact.

2. The method of removing radiation-absorptive material according toclaim 1 wherein said radiation is directed as a beam against theabsorptive material.

3. T e method of removing radiation-absorptive material according toclaim 2 which comprises the additional step of focusing the beam so thata predetermined area is exposed to the radiation.

4. The method of removing radiation-absorptive material according toclaim 1 which comprises the additional step of shielding the absorptivematerial so as to limit the area ex posed to radiation.

5. The method of removing radiation-absorptive material according toclaim 1 wherein said radiation is generated at a selected frequency andpower level and the absorptive material is vaporizable upon exposure tothe radiation.

6. The method of removing radiation-absorptive material from a basewhich is relatively nonabsorptive of the radiation according to claim 1wherein the relatively nonabsorptive base is composed of paper.

7. The method of moving radiation-absorptive material from a base whichis relatively nonabsorptive of the radiation according to claim 1wherein:

the nonabsorptive base constitutes material capable of receivingmeaningful or decorative marks thereon: and the absorptive materialtakes the form of decorative or meaningful marks, such as a typewrittencharacter.

1. The method of removing radiation-absorptive material from a basewhich is relatively nonabsorptive of the radiation which comprises thesteps of: generating a short at such energy level and pulse in the orderof milliseconds or less of substantially coherent radiation; anddirecting such radiation against the absorptive material whereby energyis absorbed therein to effect a heating and removal thereof from thebase, the base absorbing substantially a minimal amount of radiationwhereby it remains substantially intact.
 2. The method of removingradiation-absorptive material according to claim 1 wherein saidradiation is directed as a beam against the absorptive material.
 3. Themethod of removing radiation-absorptive material according to claim 2which comprises the additional step of focusing the beam so that apredetermined area is exposed to the radiation.
 4. The method ofremoving radiation-absorptive material according to claim 1 whichcomprises the additional step of shielding the absorptive material so asto limit the area exposed to radiation.
 5. The method of removingradiation-absorptive material according to claim 1 wherein saidradiation is generated at a selected frequency and power level and theabsorptive material is vaporizable upon exposure to the radiation. 6.The method of removing radiation-absorptive material from a base whichis relatively nonabsorptive of the radiation according to claim 1wherein the relatively nonabsorptive base is composed of paper.
 7. Themethod of moving radiation-absorptive material from a base which isrelatively nonabsorptive of the radiation according to claim 1 wherein:the nonabsorptive base constitutes material capable of receivingmeaningful or decorative marks thereon: and the absorptive materialtakes the form of decorative or meaningful marks, such as a typewrittencharacter.